Improving high efficiency reactivity controlled compression ignition combustion with diesel and gasoline direct injection

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Abstract
Computational studies of heavy-duty diesel engine reactivity controlled compression ignition combustion employing both high pressure common rail diesel and low pressure gasoline direct injection were conducted to examine the benefits of using gasoline direct injection compared to port injected gasoline in improving engine performance. In the current study, multi-dimensional modeling using a discrete multi-component fuel vaporization version of the KIVA-3V code was used to examine gasoline direct injection strategies to improve CO and unburned hydrocarbon emissions while maintaining low indicated specific fuel consumption. For a 9 bar indicated mean effective pressure, 1300 r/min operating condition the engine-out CO and unburned hydrocarbonons were reduced by 27.1% and 7.1%, respectively, while engine-out NOx and soot emissions were maintained low. The predicted indicated specific fuel consumption was 159 g/kW h and the maximum pressure rise rate was 6.1 bar/°, which are comparable to or lower than those of the port injected reactivity controlled compression ignition combustion case. Although further study is needed to find optimum injection strategies to improve the combustion efficiency of reactivity controlled compression ignition combustion using gasoline direct injection, the current results show that direct-injecting both high and low reactivity fuels has the potential to reduce CO and unburned hydrocarbon emissions without sacrificing the thermal efficiency benefit of reactivity controlled compression ignition. Moreover, the reduced maximum pressure and pressure rise rate indicates the possibility of improved brake efficiency in reactivity controlled compression ignition combustion and lowered exhaust gas recirculation requirements. The study also explored the use of a low pressure gasoline direct injection injector for the diesel fuel and found that similar results were obtained to those with the high pressure common rail injector. This indicates that reactivity controlled compression ignition combustion is controlled by the global equivalence ratio and fuel reactivity stratification rather than by the location of the stratification in the combustion chamber. This indicates that the complexity and cost of the injection system can be reduced considerably.

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